The present invention relates to a container-piling spreader.
Spreaders are used for the loading and unloading of containers. As shown in FIGS. 17 and 18, the spreader body 102 of a spreader is as large as the top area of a container, and twist locks 103 and guide flippers 104 are arranged at the four corners of the spreader body 102.
To hoist a container C with such a spreader, a crane (not shown) winds down wire ropes 105 to let the spreader down. The guide flippers 104 position the spreader onto the container, and the twist locks 103 engage the four corners of the container C. The crane hoists up and carries the container C to its appointed place.
A number of containers are often piled up in storage yards. To place a container on containers already piled, it is necessary to position the container exactly on the immediately lower container. The present invention relates to a spreader suitable to such positioning.
Positioning means for piling up containers are disclosed in Japanese Patent No. 2601394 (prior art I) and Japanese Utility Model Registration No. 2529048 (prior art II).
An embodiment of the prior art I is illustrated in FIG. 19. Guide flippers 116 are ascendable and descendable by elevating devices 115 mounted on the spreader, and so arranged that they can be positioned at the four corners of the spreader. While a container C is hoisted by the spreader, the elevating devices 115 lower the guide flippers 116 so as to protrude their slightly expanded lower portions 117 beyond the bottom of the container C, and the flippers 116 are locked by locking devices such as hooks, magnets, pins, or tying ropes.
In accordance with the prior art I, containers can be piled up as follows. As shown in FIG. 19(a), while the guide flippers 116 are in their upper positions, they are locked at the four corners of the spreader body 111 by the locking devices. Then, as shown in FIG. 19(b), the spreader body 111 is lowered on a container C, and the twist locks 119 are, by remote control, engaged with the metal fittings on the container C to hoist it. Next, as shown in FIG. 19(c), the guide flippers 116 are lowered by the elevating devices 115 until the slightly expanded lower portions 117 protrude beyond the bottom of the container C. The guide flippers 116 are locked to the four corners of the container C by the locking devices.
Then, the container C is carried by the crane to and above another container C1. When the container C is lowered onto the container C1, the guide flippers 116 guide and position the container C exactly on the container C1.
In an embodiment of the prior art II, the spreader comprises a spreader body, guide frames with guide flippers for engaging and positioning a container, elevating devices to support the guide frames under the spreader body, winches mounted on the spreader body, and wire ropes which go from the winches in the longitudinal direction of the spreader body to one side of the spreader body, and down to the guide frame on the side, and further to the guide frame on the opposite side to be connected thereto.
According to the prior art II, the guide flippers are locked onto the bottom portions of a container by the wire ropes, but its method of piling a container on another is the same as the method of the prior art I.
The anticipated shortcomings of the prior art I are as follows:
(a) Because the guide flippers 116 are locked, or fixed, to the bottom corners of a container G, which is hoisted by the spreader, by locking devices such as hooks or pins, large vertical and horizontal forces occur on the guide flippers 116 when the container C is lowered onto the lower container C1. These forces often cause positional slippage of the lower container C1 or damage to the guide flippers 116 and the container C. PA1 (b) To lock the guide flippers 116 and their guide frames onto the container C by hooks, pins, or the likes, actuators, such as cylinders and pins, and other components are necessary, which makes the locking devices complex and the ascending/descending portions heavy, which in turn makes the elevating and other devices large, which further in turn requires a crane of large capacity. Some pins for locking the guide flippers 116 will not enter the holes of the metal fittings on the bottom corners of a container, if it is deformed. PA1 (c) As it is difficult to take appropriate preventive measures for the hooks and pins against excessive forces, they have to be given relatively large strength, which makes them and their related members larger and heavier. PA1 (d) Because the locking devices of the guide flippers, which are exposed to large external forces and shocks, are complex and no preventive measures are taken against such forces and shocks, the spreader has a relatively short operating life due to abrasion and fatigue. In addition, electric components such as sensors mounted on the guide flippers to regulate the timing of the operations of hooks, pins, and so on are generally susceptible to shocks; therefore, they tend to raise the failure rate of the spreader system and increase the down time of the crane itself. PA1 (e) Because the guide flippers are pulled, in the longitudinal direction of the container, onto the container surfaces by the tension of the wire ropes alone, and the spans of the wire ropes are large (about 12 m), the pulling forces on the guide flippers are often disturbed by the deflection and vibration due to the rope sags. As the rope spans are large, it is necessary to apply large tension to the wire ropes; therefore, it is necessary to take some measures to prevent the guide frames from being drawn upward by the rope tension. PA1 (f) When the guide frames are lowered and raised, the protrusions and door knobs on the surfaces of the container may interfere with the downward and upward movement of the guide frames.
The anticipated shortcomings of the prior art II are as follows:
In accordance with the above, the object of the present invention is to provide a container-piling spreader which does not cause positional slippage of lower containers, is easy to position its guide flippers on a container, has simple and strong structure without dispensable locking means, guides containers reliably, and is safe to operate.